1. Field of the Invention
The present invention relates to a check valve and a fuel injection pump incorporating the same for an internal combustion engine.
2. Description of Related Art
Conventionally, there has been proposed a check valve that permits fluid to flow only in one direction in a fluid passage. The check valve is used, for example, in a fuel injection pump for an internal combustion engine (hereinafter called merely an engine). As one of the fuel injection pumps for the engine, is known a star-shaped pump in which a plurality of plungers arranged radially around a cam pressurize fuel sucked into fuel pressure chambers each provided f or each of the plungers. The fuel pressurized in the respective fuel pressure chambers are gathered into a pressure fuel delivery passage provided in a pump housing and, then, supplied therefrom to a common rail.
A low pressure fuel passage, through which fuel is sucked into the fuel pressure chamber, is provided with a low pressure check valve and a high pressure fuel passage, through which fuel pressurized by the plunger is delivered, is provided with a high pressure check valve. In particular, in the fuel injection pump in which amount of fuel to be sucked is regulated, higher accuracy of valve opening pressure of the low pressure check valve is required so that the valve opening pressure is less fluctuated in addition to ensuring fluid tight sealing. A valve member of the low pressure check valve is formed generally in conical shape.
Further, it is a recent tendency that higher load is applied to the valve member, since higher fuel injection pressure is required to reduce emission. To this end, face pressure of seat contact between a seat of a valve seat member and a valve of the valve member tends to be greater so that the seat of the valve seat member is more rapidly worn. As the wear is progressed, a step is formed in the seat. At this time, the valve is prone to cut or cling into the step due to pressure applied to the fuel pressure chamber. Accordingly, the valve member sticks to the step so that the fuel cannot be sucked.
An object of the invention is to provide a check valve in which the valve member are the valve seat member are less worn.
Another object of the invention is to provide a check valve in which a valve stick hardly occurs so that it operation is stable.
It is a further object to provide a fuel injection pump whose operation is reliable with a longer lifetime.
To achieve any of the above objects, the check valve has a valve seat member, which has an inner wall that forms the fluid passage, and the valve member. The inner wall is provided with first and second conical seats immediately adjacent each other. The second conical seat is positioned upstream the first conical seat. The valve member is provided at an outer circumference thereof with a conical face that comes in contact with the first conical seat for closing the fluid passage and away therefrom for opening the fluid passage.
In the check valve mentioned above, an angle of the second conical seat to an axis of the valve member is more acute than that of the first conical seat.
Since the check valve has the second conical seat, a relief angle of the valve seat member to the valve member is relatively small so that contact pressure applied to the first conical seat is uniformly dispersed and, thus, the first conical seat is less worn out.
Further, the second conical seat prevents the valve member from cutting into and sticking to the valve seat member, even if the wear has been progressed. Accordingly, an operation of the check valve is stable for a longer period of time.
It is preferable that, when the valve member is initially assembled to the valve seat member, one of axial end circumferential peripheries of the side surface comes in contact with the first conical seat, or a circumferential edge of the first conical seat on a side of the second conical seat comes in contact with the side surface. This will serve to keep a valve opening pressure of the check valve constant. Accordingly, if the check valve is applied to the fuel injection pump, this helps improve endurance and reliability of the fuel injection pump.
Further, it is preferable that the valve member has a relief conical face positioned immediately adjacent to and downstream the conical face and an angle of the relief face to an axis of the valve member is more acute than that of the control face.
Since another relief angle of the valve seat member to the valve member is also relatively small because of the relief conical face so that contact pressure applied to the first conical seat is further uniformly dispersed and, thus, the first conical seat is much less worn out.
Further, since the relief conical seat prevents the valve member from cutting into and sticking to the valve seat member, even if the wear has been progressed, an operation of the check valve is more stable for a longer period of time.
As an alternative, in the check valve having the valve seat member, whose inner wall forms a fluid passage, and the valve member, the inner wall is provided with a conical seat and a valve member is provided at an outer circumference thereof with immediately adjacent first and second conical faces. The second conical face is positioned downstream the first conical face and the first conical face comes in contact with the conical seat for closing the fluid passage and away therefrom for opening the fluid passage.
With the check valve mentioned above, an angle of the second conical face to an axis of the valve member is more acute than that of the first conical face.
Since the check valve has the second conical face, a relief angle of the valve seat member (the conical seat) to the valve member (the second conical face) is relatively small so that contact pressure applied to the conical seat is uniformly dispersed and, thus, the conical seat is less worn out.
Further, the second conical face prevents the valve member from cutting into and sticking to the valve seat member, even if the wear has been progressed. Accordingly, an operation of the check valve is stable for a longer period of time.